1. Field of the Invention
The present invention relates generally to an apparatus and a method for optically recording color image and audio signals, and more particularly is directed to an apparatus and method of this kind which are applicable to a so-called optical Write-Once system.
2. Description of the Prior Art
It has been proposed to record a color image signal and an audio signal or an optical disk with the frequency spectra shown in FIGS. 1A and 1B, respectively.
An optical recording method which employs the frequency spectrum of FIG. 1A is particularly used in the laser disk system, in which an FM signal (Y+C).sub.FM frequency modulated by a color composite signal and an FM signal A.sub.FM frequency modulated by an analog audio signal are frequency-multiplexed and then recorded on an optical disk medium.
An optical recording method which employs the frequency spectrum of FIG. 1B is similar to that used for the home VTR system, in that an FM signal Y.sub.FM frequency modulated by a luminance signal, a low-band-converted carrier chrominance signal C and an FM signal A.sub.FM frequency modulated by an analog audio signal are frequency-multiplexed and then recorded on an optical disk medium. The latter method is disclosed in greater detail in U.S. Pat. No. 3,893,163.
However, the above mentioned optical recording methods give rise to problems, particularly when the disk and the optical head that are employed have non-linear recording and reproducing characteristics. Therefore, cross modulation may be produced between the signals (Y+C).sub.FM and A.sub.FM in the case of the method using the spectrum of FIG. 1A, or among the signals Y.sub.FM, C and A.sub.FM in the case of the method using the spectrum of FIG. 1B due to deterioration of the laser beam source, whereby the signal to noise (S/N) ratio of the reproduced image is lowered.
Moreover, in the case of the method which employs the frequency spectrum of FIG. 1A, it is difficult to control the phase of the carrier chrominance signal contained in the color composite signal, and this results in poor reproducibility of the color tone.
Furthermore, in the method which employs the frequency spectrum of FIG. 1B, the luminance signal and the carrier chrominance signal are recorded in different frequency bands so that time deviation between these signals may occur during reproduction.